This invention is directed to a fluid lifting system and while it specially relates to oil recovery has it application to any fluid lifting application where passive and/or intermittent fluid recovery may be desired. In its oil field applications it is directed to wells generally defined as “stripper wells”. “Stripper wells” are wells that are not self producing because the zones of production have ceased to have sufficient pressure to drive the oil and or gas/oil mixture to surface in sufficient quantities to be commercial.
Some “Stripper Wells” are produced by pump jacks which have a lifting plunger piston for lifting the oil to the surface in incremental steps with each cycle of the lifting plunger. A pump jack has many moving parts and is designed for continuous operation for periods of time, but not one or two cycles at intermittent periods. Further they are expensive and require maintenance because of their many moving parts. The lifting plunger is a part especially subject to ware because of its constant up and down motion. When time comes to replace lifting plunger, it is expensive and the well must be shut down for the operation.
The operational costs as well as the maintenance costs for repairs on a “Stripper Well” can kill the commercial value of such a well because they are of marginal economic value and any increase in maintenance costs can kill the value of a “Stripper Well” from further recovery while valuable oil may still remain in the well.
These “Stripper Wells” over the years have become increasingly more important even as their production continues to decline because the value of oil has continued to rise. In that regard the prior art has developed numerous ways to produce such wells.
One such prior art approach has been to use a pair of u-shaped tubing with one of the pair dedicated to liquid discharge portion and the other to high pressure gas for driving the liquid portion to the surface. This prior art relies on the high pressure gas being held back while the liquid accumulates in the liquid discharged portion of the pipe and then a valve being opened to drive the liquid up hole for recovery. While this prior art was a step forward, it still provided more tubing surfaces to the well bore which is a very corrosive environment and as those skilled in the are will appreciate the less metal down hole the better. It further provided the need for a mechanism to hold the high pressure gas back while the fluid pipe was being filled at lower pressures. Any leak in the valve holding the pressured gas would cause the recovery system to fail and could cause damage to the well formation at the production zone.
Another prior art approach which attempted to eliminate the tubing exposure and increase the recovery used a first and second columns with the first column being located with in the second column having a larger diameter at the lower portion to form a storage chamber for the fluid to be recovered. In this prior art a one-way value was provided to the storage chamber and a one way valve was provided to said second column and then an gas injector for injection of gas into the annular space between the first and second tubing to drive the liquid to the surface. As this prior art was an integrated or unitized system it required that the whole system be installed as one piece (parallel installation) or pulled for repairs as one piece which added to the cost of installation and to the maintenance costs of a well. These additional costs, which has have been explained, could kill the value of the well from further recovery.
The prior art has recognized that as the increase in value of oil and its availability decreases it has become more desirable to become more efficient and find reliable means for its recovery. Some of that prior art has developed simpler and yet more reliable methods such as using a simple ball type standing valve which is opened by the rush of lifting gas and liquid for recovery and then checking the back flow back into the well until the next lifting cycle occurs. The problems with this approach is that there is no cleaning of the valve at each cycle and the valve can become stuck and corroded shut with the need for maintenance and these prior art system required the whole system to be pulled for repair as they were unitized. Also in the prior art the relative position of the valve in relation to its position to the gas injection port could set up air hammering which could cause metal fatigue and early failure of the whole system.
Other lifting systems attempted to solve the maintenance and repair aspects of system used in “Stripper wells” by using moving pistons which allowed oil to collect on top of a piston which was positioned in a well bore in a liquid pipe and then have pressurized gas injected into the liquid pipe below the piston to drive the slug of oil and piston out of the well for recovery. This system solved the problem of having to pull the whole system for repairs as the piston was intermittently at the top of the well and was readily accessible for repairs. Also these type system had the ability to perform additional monitoring functions of a well which provided additional cost reductions for the over all operation of a “Stripper well”. These piston driven systems however had some draw backs as the pressure behind these piston must be accurately controlled less they become rockets of destruction on their arrival at the ground level. To control these problems expensive force adsorbing devices were provided to handle slight excesses of force in landing these moving pistons at the top. However these systems added to the over complexity of system and added additional costs which as discussed are the “Death knell” to the “Stripper well”.
Finally the prior art whether of data gathering or plunger or pneumatic type systems were relatively expensive in equipment and man power costs and required multiple trips into the a well to install and recover for repair. In cases were multiple trips were required it required the balancing of tension in two independent pipes going into the well bore less one collapse upon the weight of the other and thus these systems were also difficult and expensive to install.